1. Field of the Invention
The present invention relates generally to the field of information storage devices, and more particularly to air bearing sliders used in such devices.
2. Background of the Art
Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write.
Recently the demand for smaller information storage devices has motivated the development of so-called micro-drives. Typically micro-drives are information storage devices that have been miniaturized and that therefore have smaller spinning disks than conventional devices. For example, a micro-drive may have disks with a diameter of less than 30 mm.
FIG. 1 illustrates a micro-drive having several conventional features. The disk drive includes a head disk assembly (HDA) 10 and a printed circuit board assembly (not shown). The HDA 10 houses at least one magnetic disk 12 having radius 14. The disk 12 contains a plurality of magnetic tracks for storing data. The tracks are typically disposed upon opposing first and second disk surfaces of the disk 12 that extend between an inner disk edge (associated with the inner diameter) and an outer disk edge (associated with the outer diameter) of the disk 12. The head disk assembly further includes a spindle motor 16 for rotating the disk 12. The spindle motor 16 includes a spindle motor hub that is rotatably attached to the HDA 10. The hub may have an outer hub flange that supports a lowermost one of the disks. Additional disks may be stacked and separated with one or more annular disk spacers that are disposed about the hub.
The HDA 10 further includes a head stack assembly HSA 20 rotatably attached to the HDA 10. The HSA 20 includes at least one head 26 for reading and writing data from and to the disk 12. The HSA 20 includes a bore, and the HSA 20 further includes a pivot bearing cartridge 22 engaged within the bore for facilitating the HSA 20 to rotate relative to HDA 10. The HSA 20 further includes a coil support 24 that extends from one side of the HSA 20 opposite head 26. The coil support 24 is configured to support a coil through which a changing electrical current is passed. The coil interacts with one or more magnets (not shown) that are attached to HDA 10, to form a voice coil motor for controllably rotating the HSA 20. The printed circuit board assembly (not shown) includes a servo control system for generating servo control signals to control the current through the coil and thereby position the head stack assembly 20 relative to tracks disposed upon surfaces of disk 12.
In a magnetic hard disk drive, the head 26 typically comprises a body called a “slider” that carries a magnetic transducer on its trailing end. The magnetic transducer typically includes an inductive write element and a magneto resistive read element. In a magnetic hard disk drive, the transducer is typically supported in very close proximity to the magnetic disk by a hydrodynamic air bearing. As the motor 16 rotates the magnetic disk 12, the hydrodynamic air bearing is formed between an air bearing surface of the slider of head 26, and a surface of the magnetic disk 12. The thickness of the air bearing at the location of the transducer is commonly referred to as “flying height.”
Magnetic hard disk drives, like the micro-drive described in the paragraphs above, however, are not the only type of information storage devices that have utilized air bearing sliders. For example, air bearing sliders have also been used in optical information storage devices to position an objective lens over non-magnetic media for optical read-back of data.
Since the flying height is a key design parameter that affects the performance of an information storage device, it is important that it not vary excessively during operation. The flying height, and therefore the spacing between the transducer or objective lens and the disk surface, depends strongly on the design of the air bearing surface. Optimally the flying height would remain constant at a desired value, but that is not achieved in practical devices. Manufacturing variations changes in the operating environment, or changes in the position of the air bearing surface of the slider tend to cause undesirable changes in flying height.
One environmental factor that can cause an undesirable change in flying height is the ambient pressure of the atmosphere. The ambient pressure is lower at high altitudes than at sea level, yet an information storage device must be designed to operate in both environments. An air bearing that is designed to minimize the effect of this environmental factor on flying height is said to have enhanced “altitude insensitivity.” A cavity that creates a region of sub-ambient pressure is an air bearing design feature that has been known in the past to enhance altitude insensitivity.
An example of a manufacturing variation that can cause an undesirable change in flying height is the longitudinal out-of-plane curvature of the air bearing surface, commonly known as the “crown” of the air bearing surface. An air bearing that is designed to minimize the effect of this manufacturing variation on flying height is said to have enhanced “crown insensitivity.” Lateral out-of-plane curvature of the air bearing surface can also vary in manufacturing. An air bearing that is designed to minimize the effect of this manufacturing variation on flying height is said to have enhanced “camber insensitivity.” Such enhanced crown insensitivity and camber insensitivity also tends to reduce flying height variation due to curvatures that may be present in the spinning disk surface.
Another example of a manufacturing variation that can cause an undesirable change in flying height is the pre-load force (also known as “gram load”) that presses the air bearing slider against the spinning disk surface during operation. An air bearing that is designed to minimize the effect of this manufacturing variation on flying height is said to have enhanced “gram load insensitivity”.
An undesirable change in flying height can also result from a change in the linear velocity of the disk surface that is experienced by the air bearing slider during operation. Although the spindle motors that rotate the disk or disks in information storage devices are typically able to control the angular velocity of the spinning disk within a tight tolerance, the linear velocity of the disk surface at the outer diameter (OD) of the disk is typically much higher than the linear velocity of the disk surface at the inner diameter (ID) of the disk. As a result, the flying height may tend to vary depending on the radial position of the slider relative to the disk. An air bearing that is designed to minimize the effect on flying height due to a change in linear disk velocity is said to have an acceptably “flat flying height profile.”
The miniaturization that is characteristic of micro-drives exacerbates several of the challenges to air bearing design. For example, in a micro-drive the linear velocity of the miniaturized disk at the ID is relatively low compared to that in a conventional disk drive. Micro-drives may also employ miniaturized recording heads, for example comprising so-called “pico” sliders or “femto” sliders. Such sliders make available a smaller total footprint for the air bearing surface than larger sliders, and therefore confine air bearing design to a smaller physical space. The resulting reduction in slider length challenges air bearing designers to give the air bearing adequate pitch stiffness to resist applied pitch torques. The resulting reduction in air bearing width challenges air bearing designers to give the air bearing adequate roll stiffness to resist applied roll torques.
Micro-drives also typically must be designed to survive high acceleration mechanical shocks because they are destined for use in consumer electronic devices that are portable. To meet such a survival specification, the micro-drives almost invariably employ a ramp to load/unload recording heads to/from proximity to the surface of the disk when the micro-drive is powered on/off. Ramp load/unload presents additional challenges to the air bearing designer. For example, to avoid damage to the disk surface during ramp loading, it is important that the air bearing establish itself quickly despite any initial pitch bias and/or initial roll bias that would otherwise tend to bring the slider corners in contact with the disk surface. Furthermore, to facilitate unloading it is desirable that the air bearing allows the slider to be easily lifted off the slider from the disk surface (despite any negative pressure regions of the air bearing).
Therefore, what is needed in the art is an air bearing design that can provide an adequately flat flying height profile, for example in a micro-drive information storage device utilizing ramp load/unload of the slider, and is adequately insensitive to one or more factors affecting flying height variation.